Recently, a CCD sensor has been widely used as a photoelectric transducer in image reading apparatus such as facsimile, scanner, etc. This type of CCD sensor has been variously modified and large scale CCD sensors are available at present.
With increasing demands of high speed operation, high quality image and color image processing for image reading apparatuss, importance of the processing technique for signals output from CCD sensors has increased. To process such signals output from CCDs at a high level, exclusive use large scale integrated circuits (hereinafter refered to as LSIs) for exclusive use with the CCDs have been developed.
Further, high operation frequency and driving capacity are demanded for the construction of horizontal transfer registers of CCD sensors for HDTV (High Definition Television); and two-wire reading type CCD sensors having two horizontal transfer registers have become the leading products.
In this case, there are two systems for reading signals from CCD sensors, i.e., an opposite phase reading system and an in-phase reading system. In the opposite phase reading system, two channel signals output from two horizontal transfer registers are alternately read. In the in-phase reading system, the same number of transfer stages are provided in each of two horizontal transfer registers for reading signals in the in-phase state from start of the signal transfer to an output of the signal.
In the in-phase reading system, a conventional manner for obtaining a one-line output required to delay one channel signal by using an analog delay line, etc., and then to combine the delayed signal and the other channel signal together. While in the opposite-phase reading system, such a one-line output is obtained by directly combining two channel signals output from a CCD sensor together. This means that the in-phase reading system requires complicated signal processings in comparison to the opposite phase reading system for obtaining the one-line output. Therefore, the opposite-phase reading system was the leading system for CCD sensors heretofore.
In recent years, however, it is reported that the in-phase reading system is more effective than the opposite phase reading system from the viewpoint of circuit stability, resolution stability, etc. See "Comparison of In-Phase Reading System with Opposite Phase Reading System of Two-Wire Reading CCD for High Fidelity Television". 1990 Annual Congress of Institute of Television (ITEC '90).
Accordingly, in the case of LSIs adopted for processing output signals from CCD sensors, while a leading system for processing was so far for only output signals extracted from CCD sensors by the opposite phase reading system, it becomes also necessary to process signals extracted by the in-phase reading system; However, at the present, in order to process signals extracted by the in-phase reading system it is necessary to delay signals through one of the channels by the analog delay line, etc. as described above, because both signals from a CCD sensor through two channels are the same phase. This makes the external process complicated and lacks the general usability as LSI.
As described above, conventional integrated circuits are generally capable of processing only output signals extracted from photoelectric transducers (CCD sensors) by the opposite phase reading system; and if, it is intended to process output signals extracted by the in-phase reading system, the process will become complicated.